1. Field of the Invention
The present invention relates to a rotation sensor and method for detecting the angle of rotation of a rotating member such as a steering shaft of a motor vehicle, for example.
2. Description of the Related Art
A steering system of a motor vehicle includes a rotation sensor for detecting the rotation angle of a steering wheel, that is, a steering shaft, and an example of rotation sensor is disclosed in Unexamined Japanese Patent Publication No. 2001-099680, for example.
The rotation sensor disclosed in this publication is used for measuring rotational torque of the steering shaft. More specifically, the steering shaft has an upper shaft portion coupled to the steering wheel, a lower shaft portion connected to a steering gear unit, and a torsion bar coupling the shaft portions to each other. The rotation sensor detects an angle of relative rotation, or relative angular displacement, between the upper and lower shaft portions by using electromagnetic induction technique, and based on the detected relative rotation angle, the rotational torque of the steering shaft is measured. The measured torque is used to determine an assisting force which is to be generated by the power steering system.
This type of rotation sensor can be used not only to detect the relative rotation angle as mentioned above but also to detect the angle of rotation of the steering shaft. Such a rotation sensor basically includes a rotor mounted to the steering shaft, a stator surrounding the rotor, an exciting coil contained in the stator for forming a magnetic circuit between the stator and the rotor, and metal layers formed on an outer peripheral surface of the rotor at regular intervals in a circumferential direction thereof for cutting across part of the magnetic flux of the magnetic circuit.
Thus, the rotor and the stator are arranged around the steering shaft concentrically with each other, so that the rotation sensor is inevitably increased in diameter.
Also, since the rotor has the multiple metal layers distributively formed thereon, the rotor structure is complicated. Moreover, each of the metal layers needs to have a predetermined length or more in the axial direction of the steering shaft, making it impossible to reduce the axial thickness of the rotation sensor.
Further, the rotation angle of the steering shaft cannot be accurately detected.
An object of the present invention is therefore to provide a rotation sensor which is simple in structure and reduced in size and yet is capable of accurately detecting the rotation angle of a rotating member and a method of detecting the rotation angle of the rotating member.